JP2012054229A - Separator and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator excellent in shutdown property and shape stability at high temperature, and a method for producing the separator with good reproducibility.SOLUTION: In the separator, a porous membrane containing fine particles and a water-soluble polymer and a polyolefin porous membrane are laminated to each other. The fine particles substantially comprises: fine particles (a) having an average particle size of less than 0.1 μm and specific surface area of 50 m/g or more; and fine particles (b) having an average particle size of 0.2 μm or more. The weight ratio of the fine particles (b) to the fine particles (a) is 0.05-50. The weight ratio of the fine particles to the water-soluble polymer is 1-100.

Description

  The present invention relates to a separator and a manufacturing method thereof, and more particularly to a separator for a non-aqueous electrolyte secondary battery and a manufacturing method thereof.

  Non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, are widely used as batteries for personal computers, mobile phones, portable information terminals and the like because of their high energy density.

  Non-aqueous electrolyte secondary batteries represented by these lithium ion secondary batteries have high energy density. If an internal short circuit or external short circuit occurs due to damage to the battery or equipment using the battery, a large current may flow and abnormal heat generation may occur. Therefore, non-aqueous electrolyte secondary batteries are required to prevent heat generation beyond a certain level and ensure high safety. In the case of abnormal heat generation, the separator generally has a shutdown function that blocks passage of ions between the positive and negative electrodes to prevent further heat generation. Examples of the separator having a shutdown function include a separator having a porous film made of a material that melts when abnormal heat is generated. That is, in the battery using the separator, when the porous film melts and becomes non-porous during abnormal heat generation, the passage of ions can be blocked and further heat generation can be suppressed.

  As a separator having such a shutdown function, for example, a polyolefin porous film is used. A separator made of a polyolefin porous membrane can block the passage of ions (shut down) by melting and non-porous at about 80 to 180 ° C. during abnormal heat generation of the battery, and can suppress further heat generation. . However, when the temperature is further increased, a separator made of a polyolefin porous membrane may cause a short circuit due to direct contact between the positive electrode and the negative electrode due to shrinkage or membrane breakage. As described above, a separator made of a polyolefin porous film has insufficient shape stability when the temperature is further increased, and abnormal heat generation due to a short circuit may not be suppressed.

  On the other hand, a method of imparting shape stability at high temperature to a separator by laminating a porous film made of a heat-resistant material on a polyolefin porous film has been studied. As such a highly heat-resistant separator, for example, a separator in which a porous film obtained by immersing a regenerated cellulose film in an organic solvent and a polyolefin porous film are laminated is proposed (for example, Patent Document 1). reference.). Such a separator can provide a non-aqueous electrolyte secondary battery having excellent shape stability at high temperatures and higher safety, but the load of the non-aqueous electrolyte secondary battery obtained by using the separator There was a problem that the characteristics were insufficient.

  Patent Document 2 discloses a separator in which a porous film containing fine particles and a water-soluble polymer and a polyolefin porous film are laminated as a separator having excellent shape stability at high temperature in addition to shutdown property. By using the separator for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery excellent in load characteristics, cycle performance and safety is obtained. The separator includes a step of coating a slurry containing a water-soluble polymer, fine particles, and a medium on the polyolefin porous membrane, and a water-soluble polymer and fine particles by removing the medium from the obtained coated film. It can be obtained by a step of laminating the porous membrane on the polyolefin porous membrane. However, in some of the separators obtained, it may be difficult to say that the balance between shutdown property and shape stability at high temperature is sufficient. That is, there remains room for improvement from the viewpoint of stably producing a separator excellent in shutdown performance and shape stability at high temperatures.

Japanese Patent Laid-Open No. 10-3898 JP 2004-227972 A

  The objective of this invention is providing the separator for non-aqueous-electrolyte secondary batteries excellent in shutdown property and shape stability in high temperature, and the method of manufacturing this separator with sufficient reproducibility.

The present invention provides the following.
<1> A separator in which a porous film containing fine particles and a water-soluble polymer and a polyolefin porous film are laminated to each other,
The fine particles are substantially composed of fine particles (a) having an average particle size of less than 0.1 μm and a specific surface area of 50 m ² / g or more and fine particles (b) having an average particle size of 0.2 μm or more,
The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,
The separator whose weight ratio of microparticles | fine-particles with respect to a water-soluble polymer is 1-100.
<2> The separator according to <1>, wherein the specific surface area of the fine particles (b) is 20 m ² / g or less.
<3> The separator of <1> or <2>, wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol, and sodium alginate.
<4> The separator according to <3>, wherein the cellulose ether is carboxymethylcellulose.
<5> The separator according to any one of <1> to <4>, wherein the polyolefin porous membrane is a polyethylene porous membrane.
<6> A nonaqueous electrolyte secondary battery having the separator according to any one of <1> to <5>.
<7> A step of applying a slurry containing a water-soluble polymer, fine particles and a medium onto the polyolefin porous film, and a porous film containing the water-soluble polymer and the fine particles by removing the medium from the obtained coated film A separator comprising a step of laminating on a polyolefin porous membrane,
The fine particles are substantially composed of fine particles (a) having an average particle size of less than 0.1 μm and a specific surface area of 50 m ² / g or more and fine particles (b) having an average particle size of 0.2 μm or more,
The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,
The weight ratio of the fine particles to the water-soluble polymer is 1 to 100,
And the manufacturing method of the separator whose water-soluble polymer density | concentration in the sum total of a water-soluble polymer and a medium is 0.4 to 1.3 weight%.
<8> The method for producing a separator according to <7>, wherein the specific surface area of the fine particles (b) is 20 m ² / g or less.
<9> The method for producing a separator according to <7> or <8>, wherein the solid content concentration in the slurry is 6 to 50% by weight.
<10> The method for producing a separator according to any one of <7> to <9>, wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol, and sodium alginate.
<11> The method for producing a separator according to <10>, wherein the cellulose ether is carboxymethylcellulose.
<12> The method for producing a separator according to any one of <7> to <11>, wherein the polyolefin porous membrane is a polyethylene porous membrane.

  The separator of the present invention is excellent in shape stability at high temperature, and is excellent in shutdown property and air permeability. Moreover, according to the method of the present invention, the separator can be produced with good reproducibility.

The present invention will be described in detail below.
The separator of the present invention includes a porous film (hereinafter sometimes referred to as “A film”) containing a water-soluble polymer and fine particles and a polyolefin porous film (hereinafter sometimes referred to as “B film”). The separators are laminated to each other, and a step of applying a slurry containing a water-soluble polymer, fine particles and a medium to a polyolefin porous film (B film) as described later, and drying the medium from the obtained coating film It can be manufactured by a method including a removing step. The A film has heat resistance at a high temperature at which shutdown occurs, and imparts a shape stability function to the separator. The B film imparts a shutdown function to the separator by melting and becoming non-porous during abnormal heat generation. The A film and the B film described above may be stacked on each other and may be three or more layers. For example, the form etc. with which A film | membrane was laminated | stacked on both surfaces of B film | membrane are mentioned.

  First, the A film in the separator will be described. The A film is a porous film containing fine particles and a water-soluble polymer. Examples of water-soluble polymers include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, polymethacrylic acid, etc., cellulose ether, polyvinyl alcohol, sodium alginate are preferred, and cellulose ether is further included. preferable. Specific examples of cellulose ethers include carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), carboxyethyl cellulose, methyl cellulose, ethyl cellulose, cyanethyl cellulose, oxyethyl cellulose, and the like. Is particularly preferred.

  As the fine particles in the present invention, fine particles made of an inorganic material or an organic material can be used. Specific examples of organic materials include homopolymers such as styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and methyl acrylate, or two or more types of copolymers; Fluororesin such as fluoroethylene, tetrafluoroethylene-6-propylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, melamine resin, urea resin, polyethylene, polypropylene, polymethacrylate, etc. Can be mentioned. Examples of inorganic materials include calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, oxidation Examples include calcium, magnesium oxide, titanium oxide, alumina, mica, zeolite, and glass. As the material of the fine particles, an inorganic material is preferable, and alumina is more preferable. These fine particle materials can be used alone. Two or more materials can be mixed and used.

The fine particles constituting the A film are substantially composed of fine particles (a) having an average particle size of less than 0.1 μm and a specific surface area of 50 m ² / g or more and fine particles (b) having an average particle size of 0.2 μm or more. Thus, the weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50. The materials of the fine particles (a) and the fine particles (b) may be the same as each other or different from each other.

  Of the two types of fine particles, the fine particles (b) having a large particle size serve as a main skeleton in the A film and contribute to the shape stability of the A film at high temperatures. The fine particles (a) having a small particle size have an action of appropriately filling the gaps between the fine particles (b) to further increase the mechanical strength of the A film. Further, as will be described later, It also has an action of suppressing excessive penetration of the polymer into the pores of the B membrane. The A film contains both fine particles (a) and fine particles (b). When only one of fine particles (a) and fine particles (b) is used, it has both high air permeability at practical level and shutdown property while maintaining sufficient air permeability (ion permeability). Is difficult.

Fine particles (a) has an average particle size of less than 0.1 [mu] m, preferably less than 0.05 .mu.m, and a specific surface area of the fine particles (a) is 50 m ² / g or more, preferably 70m ² / g or more. Regarding the lower limit of the average particle diameter, the average particle diameter of the fine particles (a) is usually about 0.01 μm or more. Regarding the upper limit of the specific surface area, the specific surface area of the fine particles (a) is usually about 150 m ² / g or less. Examples of the shape of the fine particles (a) include a spherical shape and a bowl shape. If the fine particles (a) do not satisfy both the average particle size of less than 0.1 μm and the specific surface area of 50 m ² / g or more, the shutdown property (non-porous B film) of the separator becomes insufficient. Here, the specific surface area of the fine particles (a) is a value measured by the BET measurement method. The average particle diameter d (μm) of the fine particles (a) is a value obtained by the following formula using the BET specific surface area B (m ² / g) and the true density D (g / m ³ ) of the fine particles. .

Average particle diameter d (μm) = 6 × 10 ⁶ / (B × D)

On the other hand, the fine particles (b) have an average particle size of 0.2 μm or more, preferably 0.25 μm or more. When the average particle size of the fine particles (b) is less than 0.2 μm, the shrinkage during heating of the A film cannot be sufficiently suppressed, and the shape stability at high temperature becomes insufficient. The specific surface area of the fine particles (b) is not particularly limited, but is preferably 20 m ² / g or less, particularly preferably 10 m ² / g or less. Regarding the upper limit of the average particle diameter, the average particle diameter of the fine particles (b) is usually about 1.0 μm or less. Regarding the lower limit of the specific surface area, the specific surface area of the fine particles (a) is usually about 4.0 m ² / g or more. Examples of the shape of the fine particles (b) include a spherical shape and a bowl shape. The average particle size of the fine particles (b) is 25 particles by arbitrarily extracting 25 particles with a scanning electron microscope (SEM) and measuring the particle size (diameter) of each particle. It is a value calculated as an average value of. When the shape of the fine particles (b) is other than a spherical shape, the length in the direction showing the maximum length of the particles is defined as the particle size. The specific surface area of the fine particles (b) is a value measured by the BET measurement method.

  In the A film, the weight ratio of the fine particles (b) to the fine particles (a) (the weight ratio of the fine particles (b) when the fine particles (a) is 1) is 0.05 to 50, preferably 0. 0.1 to 15, particularly preferably 0.2 to 10. If the weight ratio is less than 0.05, the thermal contraction of the A film cannot be sufficiently suppressed, the shape stability at high temperature becomes insufficient, and if it exceeds 50, the shutdown performance of the separator is impaired.

  In addition, fine particles other than the fine particles (a) and the fine particles (b) (hereinafter may be referred to as “other fine particles”) may be included as long as the effects of the present invention are not significantly impaired. The proportion of the content of other fine particles in the A film is preferably 100% by weight or less (including 0% by weight) with respect to the total weight of the fine particles (a) and (b), and is 50% by weight. More preferably (including 0% by weight).

  The thickness of the A film is usually 0.1 μm or more and 20 μm or less, preferably 2 μm or more and 15 μm or less. If it is too thick, the load characteristics of the battery may be reduced when a non-aqueous electrolyte secondary battery is manufactured. If it is too thin, the polyolefin porous membrane may be thermally contracted when abnormal heat generation of the battery occurs. There is a possibility that the separator shrinks without being able to resist. When the A film is formed on both surfaces of the B film, the thickness of the A film is the total thickness of both surfaces.

  The A film is a porous film, and the pore diameter is preferably 3 μm or less, more preferably 1 μm or less, as the diameter of the sphere when the hole is approximated to a sphere. If the average pore size or the pore size exceeds 3 μm, a short circuit may occur when the carbon powder, which is the main component of the positive electrode or the negative electrode, or a small piece thereof falls off. Further, the porosity of the A film is preferably 30 to 90% by volume, more preferably 40 to 85% by volume.

Next, the B film in the separator will be described. The B film is a polyolefin porous film and does not dissolve in the electrolyte solution in the non-aqueous electrolyte secondary battery. The B film preferably contains a high molecular weight component having a molecular weight of 5 × 10 ⁵ to 15 × 10 ⁶ . Examples of the polyolefin include a homopolymer or a copolymer obtained by polymerizing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. The B film preferably contains polyethylene or polypropylene, more preferably contains high molecular weight polyethylene having a weight average molecular weight of 1 × 10 ⁵ or more, and contains ultra high molecular weight polyethylene having a weight average molecular weight of 5 × 10 ⁵ or more. Even more preferred.

  The porosity of the B film is preferably 20 to 80% by volume, more preferably 30 to 70% by volume. If the porosity is less than 20% by volume, the amount of electrolyte retained may be small, and if it exceeds 80% by volume, non-porous formation at a high temperature that causes shutdown will be insufficient, and current will be generated when abnormal heat generation of the battery occurs. May not be able to be blocked.

  The thickness of B film is 4-50 micrometers normally, Preferably it is 5-30 micrometers. If the thickness is less than 4 μm, the shutdown may be insufficient, and if it exceeds 50 μm, the thickness of the entire separator is increased and the electric capacity of the battery may be decreased. The pore size of the B film is preferably 3 μm or less, and more preferably 1 μm or less.

  The B membrane has a structure having pores connected to the inside thereof, and allows gas and liquid to pass from one surface to the other surface. The air permeability of the B film is usually 50 to 400 seconds / 100 cc as a Gurley value, and preferably 50 to 300 seconds / 100 cc.

The method for producing the B film is not particularly limited. For example, as described in JP-A-7-29563, a plasticizer is added to polyolefin to form a film, and then the plasticizer is removed with an appropriate solvent. As described in JP-A-7-304110, a film made of polyolefin produced by a known method is used, and a structurally weak amorphous portion of the film is selectively stretched to form fine pores. The method of forming is mentioned. In addition, for example, when the B film is formed from an ultrahigh molecular weight polyethylene and a polyolefin containing a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, it is produced by the following method from the viewpoint of production cost. Is preferred.
Specifically, (1) 100 parts by weight of ultrahigh molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and 100 to 400 parts by weight of an inorganic filler such as calcium carbonate are kneaded to polyolefin resin. Step (2) for obtaining a composition Step (3) for forming a sheet using the polyolefin resin composition (3) Step for removing inorganic filler from the sheet obtained in Step (2) (4) Obtained in Step (3) A method comprising a step of obtaining a B film by stretching the obtained sheet, or (1) 100 parts by weight of ultrahigh molecular weight polyethylene, 5 to 200 parts by weight of a low molecular weight polyolefin having a weight average molecular weight of 10,000 or less, and an inorganic filler 100 Step of kneading ˜400 parts by weight to obtain a polyolefin resin composition (2) Step of molding a sheet using the polyolefin resin composition (3) Step The method comprising the step of obtaining the obtained step (4 to obtain a stretched sheet and stretching the sheet) Step (3) removing the inorganic filler from the resultant stretched sheet and film B 2).

  In addition, about B film, the commercial item which has the characteristic of the said description can be used.

  The A film and B film described above are laminated together to form a separator. The separator may include a porous film other than the A film and the B film, for example, a porous film such as an adhesive film and a protective film as long as the object of the present invention is not significantly impaired.

  The total thickness of the separator (the total thickness of the A film + the B film) is usually 5 to 80 μm, preferably 5 to 50 μm, and particularly preferably 6 to 35 μm. If the thickness of the whole separator is less than 5 μm, the film is likely to break, and if it exceeds 80 μm, the electric capacity of the battery may be reduced. The porosity of the entire separator is usually 30 to 85% by volume, preferably 35 to 80% by volume. When a non-aqueous electrolyte secondary battery is manufactured using the separator of the present invention, high load characteristics can be obtained, but the air permeability of the separator is preferably 50 to 2000 seconds / 100 cc, more preferably 50 to 1000 seconds / 100 cc. preferable. If the air permeability is 2000 seconds / 100 cc or more, the ion permeability of the separator and the load characteristics of the battery may be lowered.

  The dimension retention rate of the separator at a high temperature at which shutdown occurs is 90% or more, preferably 95% or more. The size maintenance ratio of the separator may vary depending on the MD direction and the TD direction of the B film. In this case, a smaller value of the dimension maintenance ratio of the B film in the MD direction and the dimension maintenance ratio in the TD direction is set to a smaller value. Use. Here, the MD direction refers to the long direction during sheet forming, and the TD direction refers to the width direction during sheet forming. If the dimensional maintenance ratio is less than 90%, a short circuit may occur between the positive and negative electrodes due to thermal contraction of the separator at a high temperature at which shutdown occurs, and as a result, the shutdown function may be insufficient. Note that the high temperature at which shutdown occurs is a temperature of 80 to 180 ° C., and usually about 130 to 150 ° C.

Next, the manufacturing method of a separator is demonstrated.
The separator of the present invention is a method comprising a step of coating a slurry containing a water-soluble polymer, fine particles and a medium (slurry for forming an A film) on the B film, and a step of removing the medium from the obtained coated film. Can be manufactured. The coating film is a film coated on the B film. By removing the medium from the coating film, a porous film (A film) containing a water-soluble polymer and fine particles is obtained, and the A film is laminated on the B film. It is presumed that when the coating film dries, a gap is formed around the fine particles and an A film is generated. If the slurry does not contain fine particles, a porous film cannot be obtained. The slurry may be applied to both sides of the B film, and the A film may be formed on both sides of the B film.

  The slurry in the method of the present invention, for example, dissolves or swells a water-soluble polymer in a medium (a liquid in which a water-soluble polymer swells may be used if it can be applied), and further adds fine particles thereto and mixes until uniform. It can be obtained by the method. The mixing method is not particularly limited, and conventionally known dispersers such as a three-one motor, a homogenizer, a media type disperser, and a pressure disperser can be used.

The fine particles in the slurry are substantially composed of fine particles (a) having an average particle size of less than 0.1 μm and a specific surface area of 50 m ² / g or more and fine particles (b) having an average particle size of 0.2 μm or more. The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50, and the weight ratio of the fine particles to the water-soluble polymer is 1 to 100.
As the medium, water or an organic solvent such as ethanol or isopropanol, or a mixed solvent of water and an organic solvent such as ethanol is used.

  The water-soluble polymer, fine particles (a), and fine particles (b) contained in the slurry for A film formation are the same as those described in the above separator. As the water-soluble polymer, cellulose ether, polyvinyl alcohol and sodium alginate are preferable, and CMC is particularly preferable. As the fine particles (a) and fine particles (b), fine particles made of an inorganic material or an organic material can be used. As the material for the fine particles, an inorganic material is preferable, and alumina is particularly preferable. The materials of the fine particles (a) and the fine particles (b) may be the same as each other or different from each other.

  Moreover, other fine particles other than the fine particles (a) and the fine particles (b) may be contained within a range not significantly impairing the object of the present invention. The ratio of the content of the other fine particles in the slurry is preferably 100% by weight or less (including 0% by weight), preferably 50% by weight or less, based on the total weight of the fine particles (a) and (b). More preferably (including 0% by weight). In addition, a surfactant, a pH adjuster, a dispersant, a plasticizer, and the like can be added to the slurry as long as the object of the present invention is not significantly impaired.

  As described above, when a slurry containing a water-soluble polymer, fine particles, and a medium is applied onto a polyolefin porous film in a conventional separator manufacturing process, the water-soluble polymer in the slurry and the medium are finely divided into the polyolefin porous film. There is a problem that the water-soluble polymer precipitates in the pores by excessively entering the pores and being dried in that state. In the method of the present invention, since the fine particles (a) contained in the slurry have a large specific surface area, the medium and the water-soluble polymer can be adsorbed and held on the surfaces of the fine particles (a). Due to the size of the fine particles (a) themselves, it is difficult to physically enter the pores of the B film. As a result, when the slurry contains fine particles (a), the fine particles (a) suppress excessive entry of the water-soluble polymer into the pores of the B film. On the other hand, since the fine particles (a) have a small particle size and are bulky, when the slurry contains only the fine particles (a) without containing the fine particles (b), the thickness is larger than the weight of the formed A film. As a result, the porosity of the A film increases, and the A film's dimensional maintenance at high temperatures and mechanical strength are impaired. Therefore, the weight ratio of the fine particles (b) to the fine particles (a) (the weight ratio of the fine particles (b) when the fine particles (a) is 1) is 0.05 to 50, preferably 0.1 to 0.1. 15 and particularly preferably 0.2 to 10. When the weight ratio of the fine particles (b) to the fine particles (a) is in the above range, the thickness of the A film can be kept moderate, the thermal shrinkage of the A film can be suppressed, and the A film has sufficient mechanical properties. Can have strength.

  The concentration of the water-soluble polymer in the sum of the water-soluble polymer and the medium in the slurry is 0.4% by weight or more and 1.3% by weight or less (based on the weight of the water-soluble polymer and the medium), preferably 0.4% by weight. % To 1.0% by weight. When the concentration of the water-soluble polymer is less than 0.4% by weight, the effect of adsorbing and holding the water-soluble polymer by the fine particles (a) is insufficient, and the adhesion of the coating film is poor. Peeling may occur, and the A film as a continuous film may not be formed on the B film. When the content exceeds 1.3% by weight, the shutdown performance of the obtained separator may be deteriorated. In addition, the molecular weight of the water-soluble polymer can be appropriately selected so as to obtain a slurry viscosity suitable for coating.

  The solid content concentration in the slurry (the total concentration of the fine particles (a) and fine particles (b) with respect to the slurry) is preferably 6 to 50% by weight, and more preferably 9 to 25% by weight. If the solid content concentration is less than 6% by weight, it is difficult to remove the medium from the slurry, and if it exceeds 50% by weight, the slurry must be applied thinly on the B film, which is difficult to apply.

  In manufacturing the A film, when the A film forming slurry is applied on the B film, the slurry enters the pores (voids) of the B film, and the water-soluble polymer in the slurry is precipitated. The A film and the B film are bonded by the “anchor effect”. At this time, if the slurry enters excessively into the pores of the B membrane, the water-soluble polymer penetrates deeper into the pores of the B membrane and then precipitates, thereby inhibiting smooth melting of the B membrane at the time of shutdown. There is a problem. This problem can be avoided by suppressing the slurry containing the water-soluble polymer from excessively entering the pores (voids) of the B film.

When the slurry contains the fine particles (a) having a sufficient specific surface area, the water-soluble polymer is adsorbed and held on the fine particles (a), and the water-soluble polymer in the slurry reaches the deep part of the pores (voids) of the B film. Infiltration can be suppressed. In order to acquire this effect, it is preferable that S value shown by a following formula is 200 m < ² > / g or more, More preferably, it is 300 m < ² > / g or more.

S = [(specific surface area of fine particles (a) (m ² / g) × parts of fine particles (a) (PHR)) + (specific surface area of fine particles (b) (m ² / g) × number of parts of fine particles (b) (PHR))] / (Parts of water-soluble polymer (PHR))

  On the other hand, when the A film contains fine particles (b) having a sufficient size as a filler, the A film can suppress thermal contraction of the B film at a high temperature at which shutdown occurs. The average particle size of the fine particles (b) is 0.2 μm or more, preferably 0.25 μm or more. If the A film does not contain fine particles (b) having an average particle size of 0.2 μm or more, it is difficult to obtain a separator that significantly suppresses thermal contraction of the B film and has sufficient dimensional maintenance. The upper limit value of the fine particles (b) is not limited as long as the shape of the A film can be maintained, but is usually 20 μm or less, preferably 5 μm or less, more preferably 1 μm or less, and even more preferably 0.00. 8 μm or less.

  The method of applying the slurry to the B film to obtain the coated film is not particularly limited as long as it is a method that enables uniform wet coating, and a conventionally known method can be adopted. For example, a capillary coating method, a spin coating method, a slit coating method, a spray coating method, a dip coating method, a roll coating method, a screen printing method, a flexographic printing method, a bar coater method, a gravure coater method, a die coater method, etc. are adopted. be able to. The thickness of the A film can be controlled by adjusting the thickness of the coating film, the concentration of the water-soluble polymer in the slurry, and the ratio of the fine particles to the water-soluble polymer. In addition, a resin film, a metal belt, a drum, or the like can be used as a support for supporting the B film.

  The removal of the medium from the coating film is generally performed by drying. As an example of a removal method, a solvent that can dissolve in the medium but does not dissolve the water-soluble polymer is prepared, and the coating film is immersed in the solvent to replace the medium with the solvent. The method of depositing a property polymer, removing a medium, and removing a solvent by drying is mentioned. When the slurry is applied on the B film, the drying temperature of the medium or the solvent is preferably a temperature that does not decrease the air permeability of the B film.

  Next, the nonaqueous electrolyte secondary battery of the present invention will be described. The battery of the present invention includes the separator of the present invention. Below, an example of a lithium ion secondary battery is demonstrated as a nonaqueous electrolyte secondary battery. Although components other than a separator are demonstrated especially, it is not limited to these.

As the nonaqueous electrolytic solution, for example, a nonaqueous electrolytic solution in which a lithium salt is dissolved in an organic solvent can be used. Examples of the lithium salt include LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li ₂ B ₁₀ Cl ₁₀ , One or a mixture of two or more of lower aliphatic carboxylic acid lithium salts, LiAlCl _{4 and the} like can be mentioned. Among these, at least one fluorine selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiC (CF ₃ SO ₂ ) _3. Containing lithium salts are preferred.

  Examples of the non-aqueous electrolyte include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di (methoxycarbonyloxy) Carbonates such as ethane; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran Esters such as methyl formate, methyl acetate and Y-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N, N-dimethylformamide and N, N-dimethylacetamide Carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by introducing a fluorine group into the above-mentioned substances can be used. Two or more of these are mixed and used.

  Among these, those containing carbonates are preferred, and cyclic carbonates and acyclic carbonates, or mixtures of cyclic carbonates and ethers are more preferred. As a mixture of cyclic carbonate and acyclic carbonate, ethylene carbonate and dimethyl have a wide operating temperature range and are hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. A mixture comprising carbonate and ethyl methyl carbonate is preferred.

As the positive electrode sheet, a sheet in which a positive electrode mixture containing a positive electrode active material, a conductive material and a binder is supported on a positive electrode current collector is usually used. As a method of supporting the positive electrode mixture on the positive electrode current collector, a method of pressure molding; a positive electrode mixture paste is obtained by further using an organic solvent, the paste is applied to the positive electrode current collector, and dried. And a method of pressing the obtained sheet and fixing the positive electrode mixture to the positive electrode current collector. Specifically, as the positive electrode active material, a material containing a material that can be doped / undoped with lithium ions, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder can be used. As the positive electrode current collector, a conductor such as Al, Ni, and stainless steel can be used, but Al is preferable in that it is easily processed into a thin film and is inexpensive. Examples of the material that can be doped / undoped with lithium ions include lithium composite oxides containing at least one transition metal such as V, Mn, Fe, Co, and Ni. Among these, lithium composite oxides having an α-NaFeO ₂ type structure such as lithium nickelate and lithium cobaltate, and lithium composite oxides having a spinel type structure such as lithium manganese spinel are preferable in that the average discharge potential is high. Can be mentioned.

  The lithium composite oxide may contain various metal elements, particularly at least selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Ag, Mg, Al, Ga, In, and Sn. The metal element is included so that the at least one metal element is 0.1 to 20 mol% with respect to the sum of the number of moles of one metal element and the number of moles of Ni in lithium nickelate. It is preferable to use composite lithium nickelate because the cycle performance in use at a high capacity is improved.

  As the binder, polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, Examples include ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic resins such as thermoplastic polyimide, polyethylene, and polypropylene.

  Examples of the conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, and carbon black. As the conductive material, each may be used alone, for example, artificial graphite and carbon black may be mixed and used.

  As the negative electrode sheet, for example, a material capable of doping and dedoping lithium ions, lithium metal, or a lithium alloy can be used. Materials that can be doped / undoped with lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds, and lower potential than the positive electrode. And chalcogen compounds such as oxides and sulfides for doping and dedoping lithium ions. As a carbonaceous material, a carbonaceous material mainly composed of graphite materials such as natural graphite and artificial graphite, because it has a high potential flatness and a low average discharge potential, so that a large energy density can be obtained when combined with a positive electrode. Is preferred.

  As the negative electrode current collector, Cu, Ni, stainless steel, or the like can be used. In particular, in a lithium ion secondary battery, Cu is preferable because it is difficult to form an alloy with lithium and it can be easily processed into a thin film. As a method of supporting the negative electrode mixture containing the negative electrode active material on the negative electrode current collector, a pressure molding method; a negative electrode mixture paste is obtained by further using a solvent or the like, and the paste is applied to the negative electrode current collector. Examples thereof include a method of pressing and drying the obtained sheet and fixing the negative electrode mixture to the negative electrode current collector.

  The shape of the battery is not particularly limited, and may be any of a paper type, a coin type, a cylindrical type, a rectangular shape, and the like.

  When producing a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte secondary battery separator of the present invention, the separator has a high load characteristic, and even when abnormal heat generation occurs, the separator exhibits a shutdown function, and further A non-aqueous electrolyte secondary battery that can suppress heat generation and avoid contact between the positive electrode and the negative electrode due to shrinkage of the separator even when the temperature is further increased can be obtained.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

In Examples and Comparative Examples, the physical properties of separators were measured by the following methods.
(1) Thickness measurement (unit: μm)
The thickness of the separator was measured according to the JIS standard (K7130-1992).
(2) Weight per unit (unit: g / m ² )
A sample of the obtained separator was cut into a 10 cm long square and the weight W (g) was measured. The weight per unit area (g / m ² ) = W / (0.1 × 0.1) was calculated. The basis weight of the A membrane was calculated after subtracting the basis weight of the polyolefin porous membrane (B membrane) as the substrate from the basis weight of the laminated porous film (separator).
(3) Porosity (unit: volume%)
The film was cut into a 10 cm long square, and weight: W (g) and thickness: D (cm) were measured. The weight of the material in the sample was divided by calculation, the weight of each material: Wi (g) was divided by the true specific gravity, the volume of each material was calculated, and the porosity (volume%) was obtained from the following formula. .

Porosity (volume%)
= 100-[{(W1 / true specific gravity 1) + (W2 / true specific gravity 2) + .. + (Wn / true specific gravity n)} / (10 × 10 × D)] × 100

(4) Air permeability (unit: sec / 100cc)
The air permeability of the separator was measured with a digital timer type Gurley type densometer manufactured by Toyo Seiki Seisakusho Co., Ltd. based on JIS P8117.
(5) Shutdown ultimate resistance measurement The shutdown temperature was measured with a cell for shutdown measurement (hereinafter referred to as “cell”). A 2 × 3 cm square rectangular membrane was impregnated with an electrolytic solution, and then sandwiched between two SUS electrodes and fixed with clips to prepare a cell. As the electrolytic solution, one obtained by dissolving 1 mol / L LiBF ₄ in a mixed solvent of ethylene carbonate 50 vol%: diethyl carbonate 50 vol% was used. The terminals of the impedance analyzer were connected to both poles of the assembled cell. The resistance value at 1 kHz was measured. Resistance was measured while increasing the temperature at a rate of 15 ° C./min in an oven. The maximum resistance value was defined as the ultimate resistance value. The shutdown property was evaluated according to the following criteria.
Evaluation of shutdown performance:
A: Ultimate resistance value is 500Ω or more. A: Ultimate resistance value is 200Ω or more and less than 500Ω. X: Ultimate resistance value is less than 200Ω.
Cut the film into a 15cm square, write a 10cm square square ruled line in the center, sandwich between two 0.5mm thick aluminum plates coated with a release agent, and heat in an oven heated to 60 ° C. I put it in. The temperature of the oven was raised to 150 ° C. at a rate of 1 ° C./minute and held for 10 minutes, then taken out, the square dimensions were measured, and the dimension retention rate was calculated. The calculation method of the dimensional retention rate is as follows.
Ruled line length before heating in MD direction: L1
Ruled line length before heating in TD direction: W1
Ruled line length in MD direction after heating: L2
Ruled line length in TD direction after heating: W2
Dimension retention (%) = ((L2 × W2) / (L1 × W1)) × 100

The water-soluble polymer, fine particles (a) and fine particles (b), and B film used for forming the A film are as follows.
<A film>
"Water-soluble polymer":
Carboxymethylcellulose (CMC): Serogen 4H manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
“Fine particles (a)”:
Fine particles (a1): AKP-G008 manufactured by Sumitomo Chemical Co., Ltd.
Average particle size: 0.024 μm
Specific surface area: 70 m ² / g
Particle shape: substantially spherical fine particles (a2): AKP-G15 manufactured by Sumitomo Chemical Co., Ltd.
Average particle size: 0.013 μm
Specific surface area: 149 m ² / g
Particle shape: Non-spherical

"Fine particles (b)"
Fine particles (b1): Sumiko Random AA-03 manufactured by Sumitomo Chemical Co., Ltd.
Average particle diameter: 0.42 μm
Specific surface area: 4.8 m ² / g
Particle shape: substantially spherical fine particles (b2): AKP-3000 manufactured by Sumitomo Chemical Co., Ltd.
Average particle size: 0.54 μm
Specific surface area: 4.3 m ² / g
Particle shape: Vertical

<B film>
Polyethylene porous membrane “B1”:
Film thickness: 15 μm
Fabric weight: 7g / m ²
Air permeability: 105 seconds / 100cc

“B2”:
Film thickness: 13 μm
Fabric weight: 6.5 g / m ²
Air permeability: 120 seconds / 100cc

Example 1
(1) Production of slurry The slurry of Example 1 was produced by the following procedure.
First, CMC is dissolved in a water-ethanol mixed solvent (water: ethanol = 2: 1 (weight ratio)) to obtain a CMC solution having a CMC concentration of 0.6% by weight (relative to [water-soluble polymer + medium]). It was. Next, 1000 parts by weight of fine particles (a1) and 3000 parts by weight of fine particles (b1) are added to the CMC solution (100 parts by weight of CMC), mixed, and mixed under high pressure dispersion conditions (60 MPa) using a gorin homogenizer. The slurry of Example 1 was produced by performing the process once. Table 1 shows the composition of the slurry of Example 1. The ratio of the total specific surface area (m ² / g) and the CMC weight (g) of the fine particles (a1) calculated from the charged amounts of the fine particles (a1) and CMC was 700.
(2) Manufacture and evaluation of separator B1 was used as a B film. The B film (MD direction 100 cm, TD direction 30 cm) was fixed to the drum, and a weight of 0.6 kg was suspended on the other side so that the B film was evenly loaded. A stainless steel coating bar having a diameter of 20 mm was arranged in parallel at the top of the drum so that the clearance from the drum was 40 μm. The drum was rotated and stopped so that the end of the side fixed with the B film tape was between the drum and the coating bar. While supplying the slurry prepared above onto the B film before the coating bar, the drum was rotated at 0.5 rpm to apply the slurry to one surface of the B film. After coating, rotation of the drum was stopped, and it was left in an atmosphere of 70 ° C. for 30 minutes to be sufficiently dried, thereby obtaining the separator of Example 1 in which the A film was laminated on one surface of the B film. In the obtained separator, the A film was in close contact with the B film, and peeling was not confirmed.
Table 2 shows the solid content weight ratio and physical properties of the separator obtained by the above evaluation method.

Examples 2-8
(1) Production of Slurry Example 2 to 8 were carried out in the same manner as the slurry production method of Example 1 except that the fine particles (a) and fine particles (b) shown in Table 1 were used in the proportions shown in Table 1, respectively. A slurry was obtained. Table 1 shows the concentration of each component in the slurries of Examples 2 to 8.
(2) Manufacture and evaluation of separator The same operation as Example 1 was performed except having used the slurry of Examples 2-8, and the separator of Examples 2-8 was produced. The B film used is shown in Table 2. Table 2 shows the solid weight ratio and physical properties of the separator obtained. In the separators of Examples 2 to 8, the A film adhered to the B film, and peeling was not confirmed.

Example 9
(1) Manufacture of slurry A slurry of Example 9 was obtained in the same manner as the slurry preparation method of Example 1 except that the proportions of the fine particles (a1) and fine particles (b1) were changed as shown in Table 1. Table 1 shows the concentration of each component in the slurry of Example 9.
(2) Manufacture and Evaluation of Separator An A film was laminated on one surface of the B film by performing the same operation as in Example 1 except that the slurry of Example 9 was used. The B film used is shown in Table 2. Next, the separator of Example 9 was obtained by laminating the A film on the other surface of the B film in the same manner, thereby laminating the A film on both surfaces of the B film. In the separator of Example 9, the A film adhered onto the B film, and no peeling was confirmed. Table 2 shows the solid weight ratio and physical properties of the separator obtained. In addition, the thickness of A film | membrane is the total thickness of A film | membrane provided in both surfaces.

Examples 10-12
(1) Production of slurry Slurry of Examples 10 to 12 in the same manner as the slurry production method of Example 1 except that the fine particles (a) and fine particles (b) shown in Table 1 were used in the proportions shown in Table 1, respectively. Got. Table 1 shows the concentration of each component in the slurries of Examples 10-12.
(2) Manufacture and Evaluation of Separator The same operation as in Example 9 was performed except that the slurry of Examples 10 to 12 was used to obtain separators of Examples 10 to 12 in which the A film was laminated on both surfaces of the B film. . The B film used is shown in Table 2. In the separators of Examples 10 to 12, the A film adhered onto the B film, and peeling was not confirmed. Table 2 shows the solid weight ratio and physical properties of the separator obtained. In addition, the thickness of A film | membrane is the total thickness of A film | membrane provided in both surfaces.

Comparative Example 1
(1) Manufacture of slurry The slurry of Comparative Example 1 was prepared in the same manner as the slurry preparation method of Example 1 except that only the fine particles (b1) were used as the fine particles and the other components were in the proportions shown in Table 1. Obtained. Table 1 shows the concentration of each component in the slurry of Comparative Example 1.
(2) Manufacture and Evaluation of Separator A separator of Comparative Example 1 was produced by performing the same operation as in Example 1 except that the slurry of Comparative Example 1 was used. The B film used is shown in Table 2. Table 2 shows the solid weight ratio and physical properties of the separator obtained. In the separator of Comparative Example 1, the A film adhered onto the B film, and no peeling was confirmed.

Comparative Example 2
(1) Production of slurry The slurry of Comparative Example 1 was prepared in the same manner as the slurry production method of Example 1 except that only the fine particles (a1) were used as the fine particles and the other components were in the proportions shown in Table 1. Obtained. Table 1 shows the concentration of each component in the slurry of Comparative Example 1.
(2) Manufacture and Evaluation of Separator A separator of Comparative Example 2 was produced by performing the same operation as in Example 1 except that the slurry of Comparative Example 2 was used. The B film used is shown in Table 2. Table 2 shows the solid weight ratio and physical properties of the separator obtained. In the separator of Comparative Example 2, the A film adhered to the B film, and peeling was not confirmed.

Comparative Example 3
(1) Production of slurry The same procedure as in the slurry production method of Example 1, except that the fine particles (a) and fine particles (b) shown in Table 1 were used, and the ratios of the other components were as shown in Table 1. A slurry of Comparative Example 3 was obtained. Table 1 shows the concentration of each component in the slurry of Comparative Example 1.
(2) Manufacture and Evaluation of Separator A separator of Comparative Example 3 was produced by performing the same operation as in Example 1 except that the slurry of Comparative Example 3 was used. The B film used is shown in Table 2. Table 2 shows the solid weight ratio and physical properties of the separator obtained. In the separator of Comparative Example 3, peeling of the A film was remarkable, and a continuous film could not be formed on the B film.

Comparative Example 4
(1) Manufacture of slurry The slurry of Comparative Example 4 was prepared in the same manner as the slurry preparation method of Example 1, except that only the fine particles (b2) were used as the fine particles and the other components were in the proportions shown in Table 1. Obtained. Table 1 shows the concentration of each component in the slurry of Comparative Example 1.
(2) Manufacture and Evaluation of Separator The same operation as in Example 9 was performed except that the slurry of Comparative Example 4 was used to obtain the separator of Comparative Example 4 in which the A film was laminated on both surfaces of the B film. The B film used is shown in Table 2. Table 2 shows the solid weight ratio and physical properties of the separator obtained. In addition, the thickness of A film | membrane is the total thickness of A film | membrane provided in both surfaces. In the separator of Comparative Example 4, the A film adhered to the B film, and peeling was not confirmed.

  For Examples 1, 7, 9, 10 and 12, and Comparative Examples 1, 2 and 4, the dimension maintenance rate (heating shape maintenance rate) and the SD characteristics were evaluated. The results are shown in Table 3.

  ADVANTAGE OF THE INVENTION According to this invention, in addition to the shape stability at high temperature, the separator for nonaqueous electrolyte secondary batteries excellent also in the shutdown property is provided. By using the separator of the present invention, even when abnormal heat generation occurs, the separator prevents direct contact between the positive electrode and the negative electrode, and the polyolefin porous film is made nonporous so that the insulating property is improved. A non-aqueous electrolyte secondary battery that can be maintained is obtained.

Claims (12)

A separator in which a porous film containing fine particles and a water-soluble polymer and a polyolefin porous film are laminated to each other,
The fine particles are substantially composed of fine particles (a) having an average particle size of less than 0.1 μm and a specific surface area of 50 m ² / g or more and fine particles (b) having an average particle size of 0.2 μm or more,
The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,
The separator whose weight ratio of microparticles | fine-particles with respect to a water-soluble polymer is 1-100. The separator according to claim 1, wherein the specific surface area of the fine particles (b) is 20 m ² / g or less.   The separator according to claim 1 or 2, wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol, and sodium alginate.   The separator according to claim 3, wherein the cellulose ether is carboxymethyl cellulose.   The separator according to any one of claims 1 to 4, wherein the polyolefin porous membrane is a polyethylene porous membrane.   A non-aqueous electrolyte secondary battery comprising the separator according to claim 1. A step of applying a slurry containing a water-soluble polymer, fine particles and a medium onto the polyolefin porous film, and removing the medium from the obtained coated film, the porous film containing the water-soluble polymer and the fine particles is made into a polyolefin porous film. A method for producing a separator including a step of laminating on a film,
The fine particles are substantially composed of fine particles (a) having an average particle size of less than 0.1 μm and a specific surface area of 50 m ² / g or more and fine particles (b) having an average particle size of 0.2 μm or more,
The weight ratio of the fine particles (b) to the fine particles (a) is 0.05 to 50,
The weight ratio of the fine particles to the water-soluble polymer is 1 to 100,
And the manufacturing method of the separator whose density | concentration of the water-soluble polymer in the sum total of a water-soluble polymer and a medium is 0.4 to 1.3 weight%. The method for producing a separator according to claim 7, wherein the specific surface area of the fine particles (b) is 20 m ² / g or less.   The method for producing a separator according to claim 7 or 8, wherein the solid content concentration in the slurry is 6 to 50% by weight.   The method for producing a separator according to any one of claims 7 to 9, wherein the water-soluble polymer is at least one polymer selected from the group consisting of cellulose ether, polyvinyl alcohol, and sodium alginate.   The method for producing a separator according to claim 10, wherein the cellulose ether is carboxymethyl cellulose.   The method for producing a separator according to claim 7, wherein the polyolefin porous film is a polyethylene porous film.